This invention relates in general to blood Pumps and more particularly to an implantable pump for replacement for a natural heart or for assistance to the pumping of the natural heart.
A number of designs have been developed for insertable blood pumps to replace or assist a natural heart. Typically such pumps are formed of a collapsible volume which can be filled and emptied with blood to provide pumping action. The shape has generally been ellipsoid with the mechanism for periodically collapsing the volume being pneumatic, hydraulic, or pusher plates. One such pump is the so-called Jarvik heart which employs a flexible membrane forming an inner wall of a rigid chamber, with the pumping being generated by hydraulic pressure against the flexible membrane controlled to provide appropriate stroke volume and repetition rate. Others include pumps with a roller screw, rotary cam, or magnetic actuator to actuate a pusher plate, and a high pressure pumping mechanism.
In many of these heart designs the blood is introduced into the chamber tangentially so that there is a generally rotary movement of the blood in the hemispherical chamber. Such an arrangement, coupled with the non-thrombogenic lining of the inner surface of the chamber is intended to inhibit clot formation. One problem, however, in this arrangement is that at the center of the vortex of the rotation there is a tendency for the blood to stagnate and thus provide a physical basis which can lead to formation of thrombosis. It has been suggested that a pump employing a toroidal shaped chamber completely formed of flexible material can avoid this Problem while still maintaining the generally circular flow of blood. One drawback to this configuration is the tendency of that flexible wall to kink or fold as it is contracted and expanded for pumping action. Such kinks or folds result in high local strain on the membrane material, thereby providing a limited lifetime for the pump.
It is therefore a primary object of the present invention to provide a fluid driven blood pump with a toroidal shape to avoid stagnation of portions of the blood by employing a toroidal shaped blood flow chamber.
It is another object of this invention to provide a blood pump for efficient circulation of blood employing hydraulic pumping wherein the parts of the chamber are constructed interpositioned to allow to provide for long component life.
It is finally an object of the present invention to provide a toroidal shaped Pump which not only wraps in Physical form conveniently around a cylindrical hydraulic actuator, but also provides for flexible membrane movement only on one axis, transverse to the direction of blood flow. This provides effective pump action with a toroidal blood flow, yet avoids kinking or folding, resulting in good fatigue characteristics and a long lifetime for the pump, as well as minimizing the formation of clots.